No reduction in the number of rats with pregnancies nor in the number of fetuses per pregnancy could be demonstrated when groups of Sprague-Dawley females were injected with placental tissue in various forms and then mated to Long-Evans males. The placental preparations were either: (1) homogenates of fetal placentas removed from Long-Evans rats; (2) whole cells of fetal placentas derived from the same Long-Evans male with which the injected female was mated; or (3) cells of fetal placenta (derived from the same Long-Evans male with which the injected female was mated) homogenized with Freund's adjuvant.